Quick summary of changes since v0.51:

- writing progress indicator (disabled with -p)
- recovery of broken GIFs (-r)
- write Software text chunk (disabled with -s)
- ignore Plain Text Extentions (-t)
- give usage message if called without arguments or pipe
- somewhat improved memory handling (less reallocs)

curiously though: no real bug-fixes! However, there was at least one relevant
bug-fix in zlib, so if you are using gif2png (or any other png writing program
using zlib) with a version below 0.95, you should update.

